The present invention relates to a device for instantaneously analyzing the shot by shot injection delivery supplied by an injection system used in a combustion engine. The injection systems concerned are, with equal preference, those found in vehicles equipped with a diesel engine, a gasoline engine, or an engine operating on LPG (liquefied petroleum gas), or any other type of engine.
Injection systems typically comprise one or more injection pumps whose task is to place the fuel under a pressure which currently may range from 100 to 2500 bar, one or more pressurized fuel reservoirs, one, or perhaps more, injectors per cylinder of the engine to be supplied, and a control system, increasingly often electronic, whose task is to control the value of the masses or volumes of fuel injected to suit the conditions of the engine surroundings, the characteristics of the fuel, and engine running requirements.
Current trends in injection systems are toward increasing the pressure of the fuel and the precision with which the injected quantities are controlled. Attempts are being made at optimizing any parameter which makes it possible to improve the efficiency of the engine and reduce the impact that the operation thereof has on the environment, particularly in the form of gaseous and acoustic pollution.
Measuring devices have been designed to allow the manufacturers of injection systems and of combustion engines to develop injectors and make settings and checks on conformity during manufacture and during installation for end-use.
The known measuring devices are used in conjunction with a special-purpose test rig, the role of which is essentially to turn an injection pump and secure the various elements of the injection system under test. These devices cannot be used on a fuel-injected combustion engine in nominal operation. The measurements are often made using a fluid which differs from the fuel for the injection of which the injection system was designed. That fluid is chosen to exhibit hydraulic properties similar to those of the fuel but with a higher flash point so as to minimize risks of fire and explosion. Thus, in what follows, the term fuel will be used also to denote the fluid used for carrying out delivery measurements.
The measuring apparatus includes a mechanical section and an electronic section. The mechanical section includes a securing system to hold one or more injectors, one measurement cell per injector for producing an electric image of the amount of fluid injected and a system for removing fluid.
The electronic section is generally in the form of a cabinet equipped with various means for interfacing with the operator, such as a screen and a keyboard, and with other external processing systems. The electronic section processes an electrical signal supplied by the mechanical section, controls and drives various auxiliaries concurrent with the measurement process.
The basic technique used for producing such measurement apparatus relies on measuring the displacement of a piston sliding in a liner, the assembly delimiting a deformable measuring volume into which the injected fuel is directed. Any quantity of fuel added to this volume causes a displacement of the piston which can easily be converted into an electrical signal by use of one of the numerous types of sensor available for this purpose. This provides a volumetric measurement. The conversion into a mass measurement is done by calculation, using the value of the density of the fuel. To guarantee precise calculation, the temperature of the fuel is measured in the measuring volume.
Other methods are used to obtain information of the temporal type, when reference is made to a time scale, or of angular type, when reference is made to a scale associated with the rotation of the driveshaft. There are two methods which are predominantly used. They are based on measuring a variation in instantaneous pressure and are carried out in measuring apparatuses of geometric structure different than those employing a piston. The xe2x80x9cBoschxe2x80x9d method uses a long wound tube and the xe2x80x9cZuechxe2x80x9d method uses a volume of a few hundred mm3. These methods make it possible to determine at what precise instant fuel is injected, but they give poor precision as to the amplitude of the fuel delivery. These methods therefore do not make it possible to determine precisely the quantity of fuel injected.
The known measuring devices therefore make it possible either to determine precisely the quantity of fuel injected by an injector or to determine the appearance of the curve of the delivery as a function of time. There does not yet exist any measuring apparatus that makes it possible to determine both the precise values of the injected volumes and the injection times/angles.
It is therefore an object of the present invention to provide such a measuring apparatus which therefore makes it possible to perform both these two different measurements.
To this end, the device that the present invention proposes is a device for measuring a quantity of fuel injected by an injector used in a combustion engine comprising a first measuring chamber into which the fuel is injected, a pressure sensor and a temperature sensor respectively measuring the pressure and the temperature in the first measuring chamber and means allowing this measuring chamber to be drained at least partially, an electronic section controlling the system and analyzing information received through the sensors.
According to the invention, this device comprises, downstream of the first measuring chamber, a second measuring chamber into which the fuel drained from the first measuring chamber is sent, and the volume of the second measuring chamber can vary with the displacement of a piston, the displacement of which is measured using a displacement sensor.
In this way, there is obtained a device which makes it possible to determine the delivery of fluid as a function of time and the precise quantity of fluid injected. The way in which this device works is then, for example, the way described in the paragraph below.
When the device is ready to make a measurement, that is to say when there is fluid in the first and second measuring chambers and a predetermined reference pressure has become established in the first measuring chamber, an injection is performed. This causes an increase in pressure in the first measuring chamber, the increase being associated with the quantity of fluid injected, with the characteristics of the fluid, with the environmental conditions, particularly the temperature, the initial pressure and the volume of the chamber. At the end of injection, the fluid which has been injected is drained into the second measuring chamber. The pressure in the first measuring chamber is thus returned to its initial value and this first chamber is ready to receive a second injection. The fluid which arrives in the second measuring chamber causes the volume of this chamber to increase, pushing the piston. This displacement is measured and, knowing the diameter of the piston, part of the electronic section calculates the exact volume of fluid. This measurement allows the electronic section to calibrate, at any moment, very exactly, the measurements made by the first measuring chamber.
The first measuring chamber therefore makes it possible to provide, with precision, the xe2x80x9cshapexe2x80x9d of the injection, while the second makes it possible to measure the quantity of fuel injected. The processing performed by the electronic section makes it possible to compensate for the defects of each of the measurements using the qualities of the other. The mechanical design of the device is more robust than the devices of the state of the art. It is not, in particular, necessary to use a pressure equalizing device in the second measuring chamber. The back-pressure is provided directly by the pressure of injection into the first cell, altering its draining. The piston can therefore simply be returned by a spring. As the stresses in the second measuring chamber are appreciably lower than in a chamber of the same type in the prior art, this chamber has far better resistance and wears far less quickly.
In one advantageous embodiment of the measuring device, a high-speed solenoid valve controlled by part of the electronic section, and a back-pressure regulator are arranged between the two measuring chambers for partially draining the first measuring chamber after an injection until the pressure in the first measuring chamber returns to the pressure that was in this chamber prior to this injection.
In this case, the electronic section advantageously comprises a compensating device to make it possible to take account of any pressure difference there might be in the first measuring chamber after two successive drainings.
In order to be able to drain the second measuring chamber after each displacement of the piston, and thus make measurements always starting from more or less the same initial piston position, a high-speed draining solenoid valve is advantageously provided downstream of the second measuring chamber.
As already mentioned above, the piston may be preloaded, for example by a spring, urging it toward the second measuring chamber.
In one advantageous embodiment, the piston moves in a smooth-walled cylinder and comprises an annular groove open toward the wall of the cylinder. This groove makes it possible to trap any leaks of gas or fluid there might be, preventing these leaks from disturbing the measurement. It also makes it possible to make the piston lighter. It also makes it possible to limit the area of the piston that needs to be lapped and matched. Finally, it increases the flexibility of the piston, which allows its sliding in the cylinder to be less impeded.
The piston displacement sensor used is, for example, an inductive sensor, but any other type of sensor may be used here. It is possible, for example, also to use an optical sensor, of interferometric type. Such a sensor is more precise, linear, and adds no moving mass to the mass of the piston. By contrast, its cost is higher and it is trickier to operate.
The measuring device according to the invention may advantageously comprise a cooling system for cooling the injector, the first measuring chamber, the piston and the piston displacement sensor. Thus, the temperature in the measuring device is evened out and its variations are limited, which makes it possible to increase the precision of the measurements taken. Use is then advantageously made, in the cooling system, of the same fluid as the one used for performing the injections.